The present invention generally relates to windows and, more specifically, to a method of making an impact resistant window structure especially suited for use in houses or buildings located in geographic regions susceptible to strong weather conditions such as tropical storms and hurricanes.
Impact resistant windows are desirable in many locations and situations. One application is in buildings or houses located in geographic regions which are highly susceptible to strong adverse weather conditions, such as hurricanes, involving extremely high winds. In such conditions, high winds can hurl large projectiles or debris into windows and the high winds themselves can create large pressure differentials between the inside and outside of a building. These pressure differentials can easily blow out or otherwise damage the windows of the house or building and cause injury to occupants.
Several local building codes in hurricane zones now require new windows to conform to strict standards related to the ability of the window to withstand large impacts and large pressure differentials. One standard requires windows to withstand two strikes by an 8 foot long "two by four" piece of wood traveling at 34 mph. Then, after these two strikes, the window is subjected to 4,500 positive and 4,500 negative pressure cycles at about 75 psf that simulates the eye of a hurricane passing the building. It appears that adoption of such strict standards will be universal in regions such as the southeastern portion of the United States.
One product which has successfully passed hurricane tests such as the one described above is marketed under the name "SENTRYGLAS". SENTRYGLAS is a laminated glass product which may be contained in a conventional window frame structure and includes an outer glass sheet, an outer polyester film layer and a polyvinyl butyryl layer sandwiched therebetween to adhere the polyester layer to the glass sheet. Silicone is used to secure this laminated glass product within the frame structure in a conventional manner. Although this product has passed hurricane tests, it has disadvantages associated with its relatively high cost combined with the fact that the polyester film layer scratches very easily and may not be replaced without replacing the entire glass laminate product.
One attempted solution to this problem involved laminating an additional glass layer on the opposite side of the polyester film layer to make the composite more similar to conventional laminated glass. This additional glass layer was of the same length and width dimensions as the first glass layer. However, when this modified SENTRYGLAS composite is subjected to the hurricane tests such as those mentioned above, the additional glass layer breaks and cuts or slices through the silicone sealant used to hold the composite in the frame. The glass then vacates the window and frame structure and the window therefore fails the test. This is especially true with standard lightweight vinyl or wood windows used in most residences.
In view of the problems associated with available impact resistant window structures, there is a need for an impact resistant window which can not only pass the strict hurricane test standards now being imposed but which is also more aesthetically pleasing and economical than past impact resistant windows.